Problem: Find $\log_{10} 40 +\log_{10} 25$.
Explanation: Using $\log x+\log y=\log xy,$ we get that $\log_{10} 40+\log_{10} 25=\log_{10}(40\cdot 25)=\log 1000.$ That means we want $x$ where $10^x=1000,$ which means $x=3.$ Therefore, $\log_{10} 40+\log_{10} 25=\boxed{3}.$